The present invention relates to a safety assembly for a syringe prefilled with injection liquid, in particular a medicine.
In the state of the art, a safety assembly is already known for a prefilled liquid injection syringe comprising a tubular body that forms a reservoir for the liquid, and that carries a needle for injecting the liquid and a plunger that is mounted in the body to be movable between a ready position and an end-of-injection position.
Usually, the plunger of a syringe has a drive end outside the body of the syringe and an end inside the body of said syringe that carries a piston. The drive end of the plunger is also known as a thumb rest.
Certain medical substances such as vaccines, heparins and derivatives thereof, and other accurately-dosed medicines, cannot be stored in containers or syringes made of plastics material because of the rate at which moisture is taken up, which would run the risk of compromising the composition.
Aware of these imperatives, laboratories are constrained to use only containers made of glass which presents no porosity. Given infectious virus diseases for which there is at present no antidote, safety is currently sought for providing all health care personnel with protection against any risk of possible contamination during professional accidents due to injections. This protection must come close to the 100% rate that the profession is calling for.
The problem is thus to fit a safety mechanism to syringes that are preferably made of glass, in particular syringes having capacity in the range 0.1 milliliters (ml) to 2 ml, since any type of mechanism internal to such syringes is unsuitable.
In addition, the requirement for sterility excludes any internal handling of a syringe once it has been filled.
Various solutions have been presented to laboratories and set aside for various reasons: increase in volume, modification to filling assembly lines, complex operations required of the doctor or the personnel using those proposals, pseudo-protection that is more harmful than useful.
It should be observed that numerous inventors can be criticized for their misleading use of language such as “a syringe having an automatically withdrawable needle” which, very often, turns out to be no more than a syringe which locks automatically, or a syringe having elements that can be destroyed, or having a cap or sliding tube to hide the needle after use.
In practice, a nurse holds a syringe between the index and middle fingers and presses with the thumb against the thumb rest. As a result, while the syringe is being held, the needle can be retracted only into a hollow plunger or piston, since the body of the syringe remains stationary.
In other cases, a sheath that slides longitudinally on the outside of the syringe “covers” the needle and thus in fact amounts to “retracting” the needle by advancing the sheath either manually or automatically.
Numerous patents are based on that known configuration which has been rejected by the medical profession because of the risk of the needle being pulled out or the patient suffering an incision as a result of the shock of the sheath striking the patient under the force of a spring urging the sheath into the needle-retraction position.